Hi
For desktop intel cpu's
Usually i3 is dual core and i5 4 core
But i3 has hyperthreading which makes it look like 4 cores in device manager
pentium usually has 2 core
(Ignoring changes in intel 8th generation cpu's)
BUT i5 cost more than i3 which cost more than pentium
So it depends on what you need to do with your pc which is best for you
Regards
Mike Barnes